Temperature And Moisture For The English Walnut

What amount of freezing and drouth can English walnuts stand? Under what
conditions is irrigation necessary?

The walnut tree will endure hard freezing, providing it comes when the
tree is dormant, because they are successfully grown in some parts of
the Eastern States, though not to a large extent; but the walnut tree is
subject to injury from lighter frosts, providing they follow
temperatures which have induced activity in the tree. On the Pacific
Coast the walnut is successfully grown as far north as the State of
Washington, but even in California there are elevations where frosts are
likely to occur when the tree is active, and these may be destructive to
its profit, although they may not injure the tree. You are not safe in
planting walnuts to any extent except in places where you can find trees
bearing satisfactorily. Planting elsewhere is, of course, an
enterprising experimental thing to do, but very risky as a line of
investment. Irrigation is required if the annual rainfall, coupled with
the retentiveness of the soil and good cultivation, do not give moisture
enough to carry the tree well into the autumn, maintaining activity in
the leaves some little time after the fruit is gathered.